package acm.蓝桥02;

import java.util.Scanner;

public class 翻硬币 {
    static char[] a;
    static char[] b;

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
         a= sc.nextLine().toCharArray();
         b = sc.nextLine().toCharArray();
        long res=0;
        for (int i = 0; i < a.length; i++) {
            if (a[i]!=b[i]){
                res++;
                if (i+1<a.length){
                    flip(i+1);
                }
            }
        }
        System.out.println(res);
    }
    public static void flip(int i){
        if (a[i]=='*'){
            a[i]='o';
        }else {
            a[i]='*';
        }
    }
}
